The original Dwyer Magnehelic Gage for high accuracy, guaranteed to 2% of full scale, and for the wide selection of 81 models available precisely to fit your needs. Using Dwyer's simple, anti-friction Magnehelic Gage movement, it quickly indicates low non-corrosive air or gas pressure, either positive, negative (vacuum) or differential. The design resists shock, vibration and over-pressures. No gauge fluid to evaporate, freeze or cause toxic or leveling problems. It's economical, too. The Magnehelic Gage is the industry standard for measuring fan and blower pressures, filter resistance, air velocity, furnace draft, pressure drop across orifice plates, liquid levels with bubbler systems and pressures in fluid amplifier or fluidic systems. It also checks gas-air ratio controls and automatic valves, and monitors blood and respiratory pressures in healthcare equipment. Standard model (shown in picture.)